Male longevity and mating success in relation to body size in northern corn rootworm

In insects, body size is often an important component of male lifetime mating success, especially when they are capable of multiple matings over their life. We paired a large or small male northern corn rootworm with a female of random size and noted copulation success. We observed courtship and copulation durations. We offered each male a female up to three times a week depending on available females. Of 87 males (38 large and 49 small) 72 mated successfully when first offered a female, 36 by both large and small males, resulting in smaller males having a higher frequency of female rejections. There was no difference in longevity between large (69 d) and small (74 d) males. There were 1346 mating opportunities for large (644) and small (702) males, with a mean of 19 females per male. Again, smaller (244) males had a higher frequency of unsuccessful matings than larger (131) males. For both large and small males, the frequency of unsuccessful copulations increased as males aged. For all successful pairings, courtship duration did not vary based on male size, but smaller males copulated for longer periods than larger males, primarily because copulation duration was longest for small males mating large females and shortest for large males mating small females. If resistance to Bt corn were to reduce male size, resistant males could be at a disadvantage for female ova. If resistance to Bt corn were to boost male size, resistant males could have a reproductive advantage over susceptible males.